Apparatus for the separation of particles contained in exhaust gases of internal combustion engines

ABSTRACT

The invention relates to an apparatus for the separation of particles contained in exhaust gases of internal combustion engines in which the exhaust gas flow is guided through a filter medium in which particles can be absorbed and held back ( 4 ). The invention should improve the separation in a cost effective manner with respect to conventional particle filters. In accordance with the invention, the filter medium ( 1 ) is made from a metal open-pore foam having at least two layers ( 11, 12, 13 ) which each have a thickness, porosity and/or pore size in the flowthrough direction through the filter medium which differ from one another.

The invention relates to an apparatus for the separation of particlescontained in exhaust gases of internal combustion engines, saidapparatus also usually being called a diesel particulate filter.

For these applications, predominantly those apparatus have previouslybeen used in which the separation is carried out using ceramic members,preferably made of silicon carbide. These ceramic materials areadmittedly well suited for a high-temperature use, but have somesubstantial disadvantages due to the material. This relates, on the onehand, to the large inherent mass to be recorded as a result of therelatively high density which in particular has a fuel consumptionincreasing effect on mobile use in vehicles. Ceramic materials aremoreover brittle and prone to destruction or damage in cases ofoscillating alternating load.

A further disadvantage results due to a thermal expansion which differssubstantially from metals usually used for the housings and which canonly be compensated with increased effort and/or expenditure.

Further known solutions use fiber structures. The latter requireproperties which increase the manufacturing costs. For instance, inaddition to temperature resistance, fiber structures must also achieve asufficient long-term separation capability. Such fiber structures,however, also do not have any sufficiently high strength withoutadditional measures.

A further possibility known per se is the use of particles which areused in bulk or in a local composite of the individual particles. Theinherent strength is also not sufficiently present here.

It is therefore the object of the invention to improve the separation ofparticles contained in exhaust gases of internal combustion engines in acost-effective manner.

This object is solved in accordance with the invention by an apparatushaving the features of claim 1.

Advantageous aspects and further developments can be achieved withfeatures designated in the dependent claims.

In the apparatus in accordance with the invention, exhaust gas of aninternal combustion engine containing particles is guided through afilter medium. The filter medium is made of an open-pore metal foam andis made, in this connection of at least two layers of such a foam. Thethickness, the porosity and/or the mean pore size of the individuallayers differ. For instance, the layer first flowed through by exhaustgas containing particles will have a larger thickness, a larger porosityand/or a larger mean pore size than the layer(s) subsequently flowedthrough by exhaust gas. If more than two layers form a filter medium,the respective layer thickness, the porosity and/or the mean pore sizereduce in size successively in the direction of flow.

The exhaust gas containing particles can be introduced into theapparatus via at least one inlet passage and be discharged via at leastone outlet passage after flowing through a filter medium.

The open-pore foam forming the layers for the filter medium canpreferably be made using nickel, iron or a nickel alloy or iron alloy,with in particular chromium, and optionally further alloys containingalloy elements comprising advantageous properties. Such nickel alloysshould preferably be used.

As far as possible, three layers, but a maximum of ten layers, of suchan open-pore metal foam should form a filter medium for a goodseparation capability. The layers should, as far as possible, be intouching contact with one another and hollow spaces between theindividual layers should be avoided as far as possible. For thispurpose, the layers forming the filter medium can be connected to oneanother at the outer edge which can anyway not be used for theseparation. The connection can be limited to diametrically opposed endfaces.

The layers forming the filter medium should have a total thickness of atleast 1.5 mm.

In this connection, the layer first flowed through by exhaust gascontaining particles should have at least a mean pore size of 200 μm.

It should make up at least 40% of the total layer thickness of thefilter medium formed from the layers.

A second layer flowed through after this should have a mean pore sizewhich is at least 100 μm smaller than the layer first flowed through.

A third layer, flowed through by exhaust gas last, should have a meanpore size which is in turn at least 100 μm smaller than that the layerarranged before it has.

The filter medium formed from the layers can be configured in plateshape with a planar surface.

It can, however, also be configured in tubular form and form a hollowcylinder. In this case, the interior can form an inlet passage or alsoan outlet passage. More than one outlet passage or inlet passage canalso be formed radially outwardly or also inwardly by correspondingpartition walls. With such an embodiment, no rotational symmetry has tobe observed. Different cross-sectional geometries such as square orrectangular shapes can also be selected and thus a matching to desiredinstallation conditions, for example in a motor vehicle, can be takeninto account.

A filter medium formed from a plurality of layers can also be woundaround a longitudinal axis in a spiral shape.

The filter medium and the inlet and outlet passages can be made in Ushape and in this connection exhaust gas can also flow along in U shapethrough an apparatus made in this manner, with exhaust gas also flowingsuccessively through the filter medium from an inlet passage into anoutlet passage while flowing through.

The inflow direction of exhaust gas containing particles into an inletpassage can be aligned parallel to the surface of a layer first flowedthrough by exhaust gas. The oppositely disposed front side end of suchan inlet passage can then be closed so that the whole exhaust gas volumehas to flow through the filter medium and can be discharged to ambientfree of particles via an outlet passage after this flowing through. Inthis connection, the whole length of the filter medium along an inletpassage with the corresponding surface of the filter medium flowedthrough by exhaust gas containing particles is available for theseparation. In this context, free of particles should be understood suchthat at least preset statutory provisions are observed.

It can be advantageous to reduce the free cross-section of an inletpassage in the direction with which exhaust gas containing particlesflows into the inlet passage. On the flowing of the exhaust gascontaining particles through the inlet passage, its flow speed therebyincreases as the free cross-section reduces, which results in animproved separation of particles. The reduction in the freecross-section of an inlet passage in the direction of flow can be madecontinuous in this connection. The flow speed of the exhaust gascontaining particles in the inlet passage can thus be approximatelydoubled starting from the entry into the inlet passage up to and intothe proximity of the oppositely disposed front face end of the inletpassage.

This can be achieved by a corresponding configuration of a housing withwhich the one or more inlet passage(s) can also be formed. However, acorresponding partition wall can also be interposed which brings aboutthis effect.

A further possibility consists of enlarging the total layer thickness ofa filter medium in the inflow direction of the exhaust gas containingparticles so that the free cross-section can thereby be reduced and theflow speed can be increased. In this connection, only the layer firstflowed through by the exhaust gas containing particles can becomethicker in this direction.

The filter medium can, however, also be configured such that at leastone of the layers has a porosity and/or mean pore size varying ingraduated form. This should take place such that it reduces from thefront to the rear in the inflow direction.

Such an embodiment can be combined with a previously explained one inwhich one or more inlet passages with a reduced cross-section arepresent.

In addition, the surface of the open-pore metal foam can be providedwith a coating at least regionally. For instance, only the surfacefacing outwardly in the direction of the inlet passage of the layerfirst flowed through by the exhaust gas containing particles can, forexample, be coated.

With a coating, an enlarging of the specific surface of the layer(s)and/or a catalytic effect can be achieved, which can result in anincrease of the separation capability for particles or in an improvementof the quality of the exhaust gas discharged to ambient.

The invention should be explained in more detail with reference toexamples in the following.

There are shown:

In FIG. 1, a perspective schematic representation of an example of anapparatus in accordance with the invention having a plurality of inletand outlet passages aligned parallel to one another as well as filtermedia;

In FIG. 2, an enlarged section of an apparatus in accordance withexample 1;

FIG. 3, an example having two inlet and outlet passages as well asfilter media in each case;

In FIG. 4, an example having two separate inlet passages via whichexhaust gas containing particles flows in and through two filter mediaand is discharged via a common outlet passage;

In FIG. 5, an example having a support structure;

In FIG. 6, in schematic form, an example having an inlet passage whosefree cross-section is reduced; and

In FIG. 7, in schematic form, an embodiment having a graduated porosityor a mean pore size at a filter medium.

In FIG. 1, an example of an apparatus in accordance with the inventionis shown in which exhaust gas is introduced via connection pipes and isalso discharged to ambient again. The effective part with a plurality ofinlet passages 2 and outlet passages 3, which are each separated fromone another by means of a filter medium, is disposed therebetween. Theexhaust gas containing particles can flow into the individual inletpassages, then flow through the individual filter media 1 and bedischarged via outlet passages 3. The inlet and outlet passages 2 and 3as well as the filter media 1 are aligned parallel to one another andthe whole has a square or rectangular cross-section. The inlet passages2 and the outlet passages 3 are closed mutually at their end faces todischarge the exhaust gas flow through the filter media 1 and out of theoutlet passages 3.

A structure of a filter medium, which is made with three layers 1.1;1.2; and 1.3, is illustrated with an enlarged detail of FIG. 1 such asis shown in FIG. 2. The layers 1.1; 1.2; and 1.3 are made from anopen-pore foam comprising a nickel alloy.

The layer 1.1. first flowed through in the direction of an inlet passage2, that is first flowed through by exhaust gas containing particles, hasa mean pore size of 0.8 mm.

The second layer 1.2 has a mean pore size of 0.58 mm. The layer 1.3 of afilter medium 1 arranged in the direction of an outlet passage 3 has amean pore size of 0.45 mm.

The FIG. 3 illustrates a possibility having in each case two inlet andoutlet passages 2 and 3 which are in turn separately divided from oneanother by a filter medium 1 through which exhaust gas flows for theseparation of particles. It becomes clear in this context how the flowof the exhaust gas is directed and how end-face mutually oppositelydisposed ends of inlet and outlet passages 2 and 3 are closed in agas-tight manner.

FIG. 4 shows an example having two inlet passages 2 for exhaust gascontaining particles which flows through a filter medium 1 in each caseand then particle free exhaust gas is discharged to ambient via a commonoutlet passage 3.

A possibility is shown in schematic form in FIG. 5 for an increase inthe stability or also strength by means of a support structure 4. Such asupport structure can be connected in a firmly bonded manner to a filtermedium 1 of a housing wall or to the wall of an inlet or outlet passage2 or 3. This can be achieved using webs or metal sheets which can form asupport structure 4. In this connection, the spacing of individualcomponents to one another can be observed in the long term on anapparatus in accordance with the invention. A support structure 4should, however, be configured, arranged and dimensioned such that theflow relationships for the exhaust gas are not disadvantageouslyinfluenced.

In FIG. 6, an example is shown having a free cross-section of an inletpassage 2 tapering conically in the inflow direction of exhaust gascontaining particles.

Accordingly, the flow speed of the exhaust gas containing particles canbe increased on the throughflow of the inlet passage 1 starting from theentry into the inlet passage 2 up to and into the proximity of theoppositely disposed end of the inlet passage 2. The damming effect ofthe end face of the inlet passage 2 closed in a gas tight manner actsshortly before the front face end and the flow speed is lower againthere.

The reduction in size of the free cross-section of an inlet passage 2 isindicated schematically here by an additional partition wall 5.

FIG. 7 shows an example in which a filter medium 1 configured ingraduated shape has been selected in the direction of the exhaust gascontaining particles flowing into an inlet passage 2. In thisconnection, the porosity and mean pore size at the filter medium 1reduce in size in this direction so that the flow resistance for theexhaust gas flowing through the filter medium 1 increases in thedirection of the end of the inlet passage 2. This can result in ahomogenization of the flow of the exhaust gas containing particles inthe inlet passage 2.

Only one region of the filter medium 1 can also be provided with acoating in such an embodiment, said coating in turn also being able tobe catalytically effective.

1. An apparatus for the separation of particles contained in exhaustgases of internal combustion engines, wherein exhaust gas flow of aninternal combustion engine is guided through a filter medium andparticles from the exhaust gas flow are absorbed and held back in thefilter medium, characterized in that the filter medium is made from ametal open-pore foam having at least two layers and thickness, meanporosity or mean pore size of the layers reduce in size in A throughflowdirection through the filter medium.
 2. An apparatus in accordance withclaim 1, characterized in that exhaust gas is discharged via at leastone inlet passage through the filter medium and via at least one outletpassage.
 3. An apparatus in accordance with claim 1, characterized inthat the filter medium consists of open-pore foam which is made ofnickel, iron or an alloy thereof.
 4. An apparatus in accordance withclaim 1, characterized in that the filter medium is made with up to tenlayers.
 5. An apparatus in accordance with claim 1, characterized inthat the layer first flowed through by exhaust gas containing particleshas a mean pore size of at least 200 μm.
 6. An apparatus in accordancewith claim 1, characterized in that a filter medium made of layers has atotal thickness of at least 1.5 mm.
 7. An apparatus in accordance withclaim 1, characterized in that the filter medium is made in plate form.8. An apparatus in accordance with claim 1, characterized in that thefilter medium is made in tubular form.
 9. An apparatus in accordancewith claim 1, characterized in that the filter medium is wound in aspiral manner.
 10. An apparatus in accordance with claim 1,characterized in that the filter medium, inlet passage(s) and outletpassage(s) are made in U shape.
 11. An apparatus in accordance withclaim 1, characterized in that exhaust gas containing particles isintroduced into an inlet passage having a flow direction which isaligned parallel to the surface of the layer first flowed through. 12.An apparatus in accordance with claim 1, characterize in that exhaustgas containing particles enters via inlet passages separated from oneanother and is discharged via a common outlet passage after flossingthrough at least one filter medium.
 13. An apparatus in accordance withclaim 1, characterized in that A the free cross-section of an inletpassage is made in reducing size in the flow direction of the exhaustgas containing particles.
 14. An apparatus in accordance with claim 13,characterized in that, the free cross-section of the inlet passage iscontinuously reduced in size.
 15. An apparatus in accordance with claim1, characterized in that the porosity or the mean pore size of thefilter medium in at least one of the layers reduces in size in theinflow direction of the exhaust gas containing particles into an inletpassage.
 16. An apparatus in accordance with claim 15 characterized inthat the porosity and/or mean pore size is/are reduced in size ingraduated form.
 17. An apparatus in accordance with claim 1,characterized in that the total thickness of the filter medium or thethickness of at least one of the layers is enlarged in the flowdirection of the exhaust gas containing particles flowing into the inletpassage.
 18. An apparatus in accordance with claim 1, characterized inthat the surface of the open-pore metal foam of the filter medium isprovided with a coating at least regionally.
 19. An apparatus inaccordance with claim 19, characterized in that the coating enlarges thespecific surface and/or is catalytically effective.
 20. An apparatus inaccordance with claim 1, characterized in that a support structureengages at the filter medium.